When 4-year-old Andrew Burd arrived at a hospital in critical condition in the fall of 2006, doctors didn't have a clue as to what was wrong with him. Blood tests soon revealed that he had salt poisoning, or hypernatremia. Andrew's levels were off the charts -- almost double the norm and among the highest ever recorded.

Doctors turned to Hannah Overton, a 29-year-old pregnant mother of four who was in the process of adopting Andrew. She told them Andrew had thrown a fit that afternoon after he'd been fed a full lunch. Instead of giving him more food, she said she put a few dashes of creole seasoning in a sippy cup of water.

But that didn't calm him, she said, and a few moments later he fell to the floor, vomited and complained of being cold. Overton said she suspected the flu, but after an hour and a half, Andrew's condition didn't improve. That's when she and her husband, Larry, took Andrew to the hospital.

The Overtons' story aroused the suspicions of doctors and investigators. The next day Andrew died and the devout Christian couple, which had no criminal history, became murder suspects. As the investigation continued, authorities developed a theory that Andrew's death was an intentional poisoning.

"We were just waiting for someone to look at it and say 'This is just an accident,'" Larry Overton told "20/20." "Instead, we were arrested."

To investigators, Andrew's sudden and bizarre death was no accident. Within days, the authorities had begun weaving a sinister tale of murder. They painted Hannah Overton as a pregnant mother of four young children who became overwhelmed with the arrival of a foster child.

The arrest warrants painted the Overton home as a house of horrors, where Andrew was monitored by a camera and was punished with spicy seasoning. Detectives even used the Overtons' children to build a case against them, saying unusual forms of punishment had been previously used.

"This case boils down to a woman who, basically, tortured a child," said prosecutor Sandra Eastwood, "becoming so enraged she forced him to have 23 teaspoons of hot pepper and then watching him die in agony."

A grand jury returned an indictment on capital murder. In the state of Texas, if a child younger than 6 dies at the hands of another person, it's considered a capital case. The charge carries a minimum life sentence.

Charged With Capital Murder: Rush to Judgment?
The Overtons' church community saw the accusations against Hannah and Larry as ludicrous and rallied around the couple, raising nearly $700,000 for their defense.

"What they came up with and what really happened were completely different things," said the Rev. Rod Carver.

"It's so bizarre," Noreen Carver, Rod Carver's wife, said, "because [Hannah Overton's] really the last person you would think would be charged with this type of crime."

The Overtons and their supporters claimed there was a rush to judgment -- that the authorities had never considered alternate theories. The Overtons said that in the four months Andrew had lived with them, he had exhibited excessive tantrums and obsessive eating.

Hannah says she started noticing that Andrew was hoarding food, stealing off the other children's plates and throwing tantrums after meal time was over. At times, they say, they caught him trying to eat things that weren't even edible.

"Anything that he found, he would try and put in his mouth. He would also eat the cat food, the dog food, out of the trash can," Hannah Overton told "20/20."

The Overtons believe this unexplained behavior might have been linked to Andrew's death.

"Something was wrong with Andrew. I don't know exactly how or what happened to him," Hannah Overton said. "Something caused his sodium levels to rise, and it wasn't me."

While Hannah and Larry Overton awaited separate trials, Hannah Overton gave birth to a baby girl named Emma. Child welfare services placed all five Overton children with loved ones, allowing the couple only supervised visits.

Medical Mystery or Murder?
From day one of Hannah Overton's trial in August 2007, the prosecution portrayed her as a mother who had lost control. Frustrated with a naughty child, prosecutors said, she tried to punish him with seasoning mixed in water and then neglected to get him medical attention, knowing that he was dying.

Detectives questioned why Hannah Overton hadn't called 911, instead driving Andrew to the hospital. One doctor calculated that it would take at least 23 teaspoons of creole seasoning (equivalent to 7 teaspoons of salt) to get Andrew's sodium level as high as it was when he arrived at the hospital.

Medical staff from the hospital also took the stand, testifying that they noticed bruising and scratching on the child's body when he arrived at the hospital. Prosecutors speculated these marks could be signs of abuse, or a struggle.

"Could it be that you held his nose, held his neck and made him drink this horrible concoction?" prosecutor Sandra Eastwood asked at trial.

"Absolutely not," Hannah Overton testified.

The prosecution also countered claims by the Overtons about Andrew's strange behavior. Witnesses, including Andrew's former foster mother Sharon Hamil, took the stand and told jurors the boy seemed perfectly healthy and never exhibited odd or excessive eating.

"Andrew was not a difficult child to take care of," said Hamil. "At least he was not when he was with me."

The defense presented the jury with a medical mystery. They speculated Andrew might have had Pica, an eating disorder characterized by an obsessive appetite. Witnesses outside the home had seen Andrew's bizarre habits too.

Hannah Overton told jurors that she thought the behavior was unusual, but had learned in adoption classes that children in foster care often exhibited issues with food.

When the problems escalated, she alerted Andrew's adoption agency. During the visit to the home, the caseworker mentioned Pica as a possible explanation.

Hannah said it was just a few days later that Andrew got sick and eventually died. She said she believes he may have gotten into something that morning when she wasn't watching that caused his sodium levels to rise.

Hannah insists the creole seasoning mixed with water wasn't to punish -- it was to soothe Andrew's insatiable appetite.

"My thought was that I would calm him down, appease him, give him like a broth, without giving him a tummy ache from eating more food," Hannah told "20/20."

When asked why she didn't get him help sooner, Hannah said, "We didn't know that there was anything major going on. We didn't realize how sick he was& If we had known that there was something more going on, we would have rushed to the hospital."

But Hannah Overton was convicted of capital murder and sentenced to life in prison in September 2007.

"I just kind of broke down," Larry Overton said. "And I just stared out a window for ... I don't know ... probably about an hour."

Jurors and Doctors Speak Out
To find Hannah guilty, jurors had to believe either of two scenarios -- that Hannah force-fed Andrew Burd salt knowing it would kill him or that she neglected to get medical help fast enough knowing that he was dying.

All 12 jurors agreed with the second scenario, and "20/20" spoke to two of them.

"I don't believe it was her intention to, to kill him," said juror Dora Santos. "I just feel that if Andrew would have gotten help sooner he would probably be alive today."

"I mean, she killed him because she didn't seek medical help," said juror Norma Bejarano.

Two doctors, both experts in the case -- one for the prosecution, the other for the defense -- feel Hannah Overton was wrongly convicted and spoke on camera for the first time to "20/20."

Dr. Edgar Cortes, the same pediatrician who treated Andrew at the emergency room and later consulted for the prosecution, says he always believed Andrew's death was accidental. Cortes is not being paid by the Overton defense team.

"I was stunned when I heard that [Hannah] had been given capital murder. I was just at a loss for words," Cortes said.

Cortes disagrees with the prosecution's portrayal of Andrew as perfectly healthy -- he says he saw speech and developmental problems back in 2005.

"The only physician that treated Andy while he was alive, and who was aware of the other neurological problems that he had, was me," Cortes said. "And I think that testimony might have given the jury an understanding that perhaps he was not a totally normal child."

But neither the defense nor the jury ever heard Cortes' opinions, which is the cornerstone of Hannah's appeal.

"Sounds very disingenuous," Cortes told "20/20," "I was very clear from day one and very forceful as to my opinions."

Eastwood stands by her case. "I feel very confident that I did the right thing in&presenting the evidence and having her convicted," she said. She also remains convinced that Hannah Overton withheld medical treatment in an effort to kill Andrew.

"I think she was angry, enraged, with wanting to punish him and hurt him and then realized, 'Oh my gosh, I've really hurt him.'"

Dr. Michael Moritz, a leading expert on salt poisoning at children's hospital of Pittsburgh, says, "I don't think there was any evidence at all that she did this."

Hannah's defense team hired Moritz, but never put him on the stand, believing his testimony would be repetitive. Moritz believes he knows what happened to Andrew.

"I think he was in one of his feeding binges, he was having a tantrum, and he was unsupervised for a brief period of time, and I believe that he ingested a large amount of salt." Moritz has written extensively about salt poisoning and its connection to pica.

"When I pulled all the cases of salt poisoning, they all fit the same profile," he said. "Children within that age group of two to six years of age, in foster care from abusive homes but with behavioral problems, who had history of pica, who by all accounts appeared to have voluntary ingested large amounts of sodium."

"I think most people would never suspect salt poisoning, since it's something very few pediatricians or emergency rooms in the country have ever encountered," he said.

What's Next for the Overton Family?
Larry Overton also faced a charge of capital murder, but pleaded no contest to negligent homicide in return for five years' probation.

"For me, having the chance of spending some time in jail and leaving my kids without parents was not something that I was willing to do," he said.

By pleading no contest, Larry did not have to admit guilt. "I wasn't going to plea to a deal and say I committed or did something I did not do," he said. After two years, Larry can go in front of a judge and ask to have it expunged from his record.

Since Hannah Overton's trial concluded, Larry Overton has been a single father of five. Once a month, he packs them into the family van and heads north. It's a 300-mile drive, but no one complains, because for two hours the Overton children visit their mom at a Texas prison, where she hopes her case will be overturned.

Still, Hannah Overton says she doesn't regret trying to adopt Andrew.

"I wouldn't take that away," she said. "He had brothers and sisters and a mommy and daddy, what he called his forever family, because we had to go through a lot of pain since then. It's not fair to him. Or to us."